From prior art, there are known several methods for producing such arms. A first method involves pressing two parts in sheet steel and joining the two parts along the rims. A recessed spring seat is formed in the lower part, with an opening in the upper part above the seat. The recessed mounting of the spring has the advantage that the spring will not protrude so far into the car body, i.e. the upper mounting point can be lowered giving more available room in the luggage compartment. Alternatively, a longer spring may be used allowing a longer stroke and a more comfortable ride. However, these steel arms are relatively heavy, even though being hollow. Generally, the un-sprung components of a wheel suspension should be kept as light as possible, in order to improve the road handling properties of the car. Further the hollow steel arms are apt to corrode. Another disadvantage of these arms is the involved production process, including pressing, punching, welding and painting. The production process involves several steps that must be performed at independent stations.
From the applicant's U.S. Pat. No. 6,810,586 there is known a rear control arm made from an extruded aluminum profile specially designed for the purpose. The aluminum profile has a hollow closed cross section with an optimized distribution of material. This control arm has several advantages, of which one is that it can be produced in standard machinery for cold forming, avoiding more involved processes such as welding, hydro forming, etc. Another advantage is the low weight, the stiffness caused by the shape of the profile, and the corrosion resistance from using aluminum. While this arm has proved to be a success in the market, it has a disadvantage in that the spring is mounted on the top surface of the arm limiting the space available for the spring and limiting the ground clearance.
The applicant is also the originator of another control arm, disclosed in WO 2006/046876 which is produced from an extruded aluminum profile with two channels separated by a web. This profile has a recessed spring seat. Also this arm may be produced in a compact work station using standard cold forming methods.